Showing posts with label tenable nessus. Show all posts
Showing posts with label tenable nessus. Show all posts

Wednesday, July 11, 2012

PCI Compliance Scans and Scams

HIPAA, SOX, SAS-70 - those whose business relies on hosting a website are no stranger to the regulatory schemes of trade organizations and their acronyms.

The PCI Data Security Standard is perhaps the most well known and widely adopted. PCI DSS is a set of very general outlines of security best practices for those who process and/or store credit cards using computers. Compliance is certified by a third party corporation (a Qualified Security Assessor or QSA), and demand is created by offering lower credit card transaction fees to websites who are certified as compliant. On the whole, the initiative has had some big successes. Credit card companies win by reducing incidents of fraud as more sites adopt standard security features, merchants win through reduced transaction costs and by being able to advertise a third party certification of secure site design and companies responsible for certification get to exist and create new jobs in the process. The standards have gone a long way toward getting merchants to comply with security initiatives that had little traction before - the adoption of secure encryption keys are one such example.

As with any plan, there are shortcomings. The most commonly cited shortcoming is endemic to any security certification: PCI is only a very general review of a very specific set of security vulnerabilities; typically these include widely published operating system vulnerabilities, as well as web server overflow, injection, XSS and enumeration exploits. Many users of PCI compliant sites are lulled into a false sense of protection, not understanding that certification only covers a single point in time and that changes to the site following certification could expose the site to attack. Site owners may also feel that PCI compliance has a one to one relationship with site security, seeing compliance as a replacement for ongoing review and planning. Security is best handled as part of the initial design of the code base and server architecture, with regular updates and testing to address the latest mischief.

This leads us to the issue I want to discuss in this post: the role of the third party certification companies / Qualified Security Assessors. In theory, market forces should make such organizations reliable and trust worthy. After all, a site that is hacked publicly that is certified as PCI compliant would be quite an embarrassment for the corporation providing the certification. Further, there must be some point at which the credit card companies would revoke their relationship with a QSA. In reality, the incentives work out in a way that is a bit more counterintuitive. I have yet to read of a public credit card data breach that discusses PCI compliance liability in any capacity - the embarrassment without fail falls on the agency who was retaining the information, not the companies retained to secure the data. Further, credit card companies reserve the right to charge fines to companies that are hacked and whose PCI compliance reviews failed to identify the source of intrusion. Paradoxically, if the PCI compliance reviews illustrate the flaw but it is ignored, fines are not levied. This produces an incentive for auditors to *not* find security flaws, and for credit card companies to certify organizations that are less than thorough in their reviews. There are many auditing companies out there that do a great job, but if there is one principle of human behavior worth its weight in ink, it is that human behavior follows incentives. If it doesn't seem to at first, wait.

As an engineer, I often play a role in correcting issues caught by PCI compliance firms. For the average merchant, the compliance firm provides a questionnaire confirming logistical security procedures, and then performs a scan of the website under audit. The scanning technology used is not novel or specifically designed by auditing firms. Tenable's Nessus scanner is in wide use for this purpose (tip to IT companies: if you are using an unmodified third party application as the foundation of your business while marketing yourself as having innovated that application, at least modify the reports provided by that application ... slap a logo on it, drop it into a template, maybe even add some line breaks).

My complaint is not with Tenable or those using it - Nessus is an excellent product and if you do not use it regularly within your own organization I recommend you download it immediately. The issue I have is with auditing firms who say they are scanning when they are not.

This is somewhat of a recent phenomenon as far as I can tell (I've worked with quite a few firms over the years and have only encountered this specific issue with a handful of them within the last 6 months). Essentially the scan is performed and enumerates data that would be revealed by any website - language framework version, operating system, web server version, etc. The scan than compiles a list of security vulnerabilities based on the enumerated application versions, without checking to see if those vulnerabilities are valid. So for example lets say just as an example that IIS 7.5 can be overtaken by a specific overflow vulnerability. Then let's say that Microsoft identified the issue and released a Security Bulletin / emergency patch for it. Then let's say that you patch your system, ensuring that you are no longer vulnerable. A compliance firm of the kind I am describing would provide you with a compliance report listing your site as vulnerable for that overflow.

What this means is that the auditing firm is not reviewing your site for vulnerabilities, it is gathering basic information about the software running on your server and compiling an almost random list of vulnerabilities that may or may not apply to your server.

This might sound like a trivial distinction at first. After all, vulnerabilities are vulnerabilities, right? If some of them are already patched, just move on to the ones that are not. 

The issue is with the efficacy and value of these scans. The scans are helpful when they illustrate issues that are not already apparent to the administrator, or when they confirm compliance. False positives are the worst possible outcome because they are wastes of time that provide no value whatsoever. Worse than not scanning at all, nearly all QSAs request some sort of confirmation that the false positive does not apply to the scanned server. This creates pointless busy work for administrators as they rush to provide documentation (which is not as easy as it sounds in the absence of a specific update- how do you prove a negative?). The time spent wading through bureaucracy could be spent identifying and resolving actual problems. Because the scans and auditing services provided by QSAs are not free, injury is added to insult when merchants are forced to absorb the costs of time spent attempting to keep the scan focused on actual security issues.

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